1. Field of the Invention
The present invention relates generally to input devices and, more particularly, to improvements for touch panel displays.
2. Background of the Related Art
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Input devices perform the function of providing some means for entering commands and data into a computer, data processor, or information system. A variety of input devices are currently available, including keyboards, light pens, data tablets, mice, track balls, joysticks, scanners, voice recognition devices, and touch screens. Each of these input devices exhibits various advantages and disadvantages, and the input device or devices used in any particular application are typically chosen to maximize the efficient input of information into the system.
This disclosure is primarily directed to the last of the input devices mentioned above, namely touch screens. Unlike the other input devices mentioned above, touch screens not only act as a data input device, they also act as a display unit. Essentially, a touch screen is a display unit with some form of a touch-sensitive surface. Due to this unique characteristic, touch screens are currently utilized in a variety of different applications, such as computer terminals, cash registers, automatic teller machines, and automated gasoline pumps to name just a few.
Currently, there are five different technologies used for touch screens: (1) capacitive, (2) resistive, (3) piezoelectric, (4) surface acoustic wave, and (5) light beam interruption. Although each of these different types of touch screens operate in a different manner and exhibit certain advantages and disadvantages, certain similarities exist. For example, regardless of the type of touch screen, the touch screen system typically includes a sensor unit, which senses the location touched on the display, and a controller unit, which interfaces with the sensor unit and communicates the location information to a system computer. Thus, regardless of the technology employed, each type of touch screen performs the same general function.
However, it is the differences in the way that the various types of touch screens operate that causes a designer to use one type of touch screen over another for a particular application. Resistive touch screens, for example, advantageously exhibit low cost, high touch point density, and can be operated with a gloved hand. Disadvantageously, however, resistive touch screens can be easily damaged, exhibit poor display characteristics, and must typically be calibrated when ambient temperature changes by more than 40 degrees Fahrenheit. Capacitive touch screens also provide high touch point density and low cost, but capacitive touch screens can be easily damaged, must be calibrated due to large temperature changes, and cannot be operated with a gloved hand. In contrast, surface acoustic wave touch screens have no overlay to be damaged or to reduce the visual quality of the display. However, surface acoustic wave touch screens typically exhibit the highest cost and can be falsely triggered by noise, wind, transmission signals, and insects. Thus, it can be seen that these three types of touch screens are typically not well suited for outdoor use where it is desirable for touch screens to be operated by a gloved hand and to be resistant to damage and false triggering.
Touch screens that use light beam interruption, typically called infrared touch screens, usually provide the best performance in outdoor applications. Infrared touch screens exhibit high touch point density, can be operated with heavy gloves, are relatively cost efficient, exhibit good immunity to most false trigger sources, and are extremely rugged and weather sealable.
Infrared touch screens operate in a very simple manner. Light sources, such as infrared photodiodes, are arranged in a row along two adjacent sides of the touch screen, and light detectors, such as photo detectors, are arranged opposite the light emitters along the two opposite adjacent sides of the touch screen. When an infrared touch screen is not being touched, the light beam from each of the light emitters crosses the screen and is received by the respective light detector. When someone touches the screen, one or more light beams are interrupted along each adjacent side so that the respective light detectors no longer receive the transmitted light beams. Because the signals from the light detectors are sent to the controller, the controller recognizes this signal interruption and determines the coordinates on the screen where the touch occurred.
Although infrared touch screens are typically the most suitable type of touch screen to use in outdoor applications, high ambient light conditions, such as direct sunlight, can cause an infrared touch screen to malfunction. High ambient light tends to saturate the light detectors and cause erratic operation of the touch screen. Various techniques have been used to combat this problem. For example, the protective covering which encases the light emitters and the light detectors is typically made of a red plastic material that functions as a broad band infrared filter that tends to filter out ambient light and pass infrared radiation. Also, certain ambient light compensation schemes have been developed which use a large amount of energy to drive the light emitting devices in an effort to maintain the intensity of the emitted light at a level greater than the intensity of the ambient light. Finally, structures such as awnings or shrouds have been used to shield the touch screen from extraneous ambient light.
Of course, each of these techniques exhibits certain disadvantages. In regard to the first mentioned technique, because the red plastic protective member operates as an optical filter in such a broad band, some of the optical energy in the sunlight spectrum is not rejected by the filter. Thus, high ambient light conditions can still trigger erratic operation. The second mentioned technique of boosting the energy to the light emitting devices is similarly ineffective in high ambient light conditions, because the intensity of the sunlight spectrum tends to become greater than the intensity of the light produced by the light emitters. Furthermore, such a light compensation scheme is hampered by the use of expensive light emitting and light detecting devices necessary to handle the increased energy requirements. Finally, in regard to the third mentioned technique of using a structural member to shade the touch screen, it can be readily appreciated that such structures add to the overall cost of the system. Also, in the case of small shrouds constructed to encompass only the touch screen, such shrouds can interfere with user operation and may be broken easily.
The present invention may address one or more of the problems set forth above.
Certain aspects commensurate in scope with the originally claimed invention are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.
In accordance with one aspect of the present invention, there is provided a touch screen assembly. The assembly may include an array of emitters and detectors. Each of the emitters are arranged to transmit light along a given path to one of the respective detectors. The emitters transmit light of a first wavelength band and the detectors respond to light of a second wavelength band, where the second wavelength band is broader than the first wavelength band. A spatial filter and/or a narrow band optical filter is disposed adjacent the detectors in the given path of the transmitted light. The spatial filter passes light oriented within a given angular range about the given path and rejects light oriented outside of the given angular range about the given path. The narrow band filter passes light of a third wavelength band, where the third wavelength band is narrower than the second wavelength band.